In order to safely store a file of a computer, users input an encryption key to encrypt the file and then store the encrypted file in a computer. Also, users input a decryption key to decrypt the encrypted file and execute the file. Korean Unexamined Patent Publication No. 10-2001-0093472 discloses an apparatus for encrypting and decrypting a content file.
However, in an existing file encrypting method, when a file frequently used is encrypted and stored, a decryption key of the file is demanded to a user whenever the user accesses the encrypted file, which causes inconvenience to the user. For this reason, the user sets an encryption key for encrypting a file with a simple code, and if the encrypted file outflows, the encrypted file may be easily decrypted by other persons due to such a simple encryption key.